Coaxial resonator apparatus



June 13, 1967 R CLARK 3,325,746

COAXIAL RESONATOR APPARATUS Filed March 12, 1964 4 Sheets-Sheet 1 (WAX/4L fa l/W44 155677017 02 6770 xze 37 414 005 I away/v0 IN VENTOR. WY/Vd/VJ M A 14/54 7% ia/r,

June 13, 1967 I R. N. CLARK COAXIAL RESONATOR APPARATUS 4 Sheets-Sheet Filed March 12, 1964 W M w MW. w R NZ W m m 7 WW June 13, 1967 R CLARK 3,325,746

COAXIAL RESONATOR APPARATUS Filed March 12, 1964 4 Sheets$heet 3 I? i w lk J 0 4;, 4 Am. F/WW INVENTOR.

June 13, 1967 CLARK 3,325,746

COAXIAL RESONATOR APPARATUS Filed March 12, 1964 4 Sheets-Sheet 4 CE/VTEE fi L/A/E/ our/w;- g

| edd/vd k Y 639/0 /4 (ma/0M TUBE) INVENTOR.

United States Patent 3,325,746 CQAXIAL RESONATOR APIARATUS Raymond N. Clark, Cherry Hill, N.J., assignor to the United States of America as represented by the Secretary of the Air Force Filed Mar. 12 1964, Ser. No. 351,574 2 Claims. (Cl. 330-56) ABSTRACT OF THE DISCLOSURE An input or output circuit for vacuum tubes in high powered, very high and ultra high frequency amplifiers consisting of tunable coaxial line sections coupled such that the coupling remains essentially constant when the circuit is tuned over a prescribed band of frequencies.

This invention relates to electrical apparatus, and more particularly to a coaxial resonator circuit with novel tuning and loading means.

This invention has utility in high powered, very high and ultra high frequency amplifiers, and in other communication applications. In ultra high frequency amplifiers utilizing single ended vacuum tubes of coaxial construction, it is necessary to have continuous tuning over a prescribed band of radio frequencies, and to have adjustable input and output coupling. Prior art coaxial resonator circuits have no provisions for compensating for the change in loading due to such high frequency tuning.

Accordingly, it is a principal object of this invention to provide an improved coaxial resonator output circuit whereby the degree of coupling (loading) remains essentially constant as the resonator is tuned over the band of operating frequencies.

Another principal object of this invention is to provide an improved coaxial resonator input circuit whereby the degree of coupling (matching) remains essentially constant as the resonator is tuned over the prescribed band of frequencies.

Still another principal object of this invention is to provide an improved coaxial resonator circuit wherein the degree of coupling can be varied without any appreciable detuning of the resonant circuit.

Other objects, features and advantages of this invention will suggest themselves to those skilled in the art and will be apparent from the following description of the invention taken in connection with the accompanying V drawings in which:

'nator;

FIG. 2 is a typical plate-to-ground reactance vs. frequency curve;

FIG. 3 is a resonator current vs. frequency curve;

FIG. 4 is a plot of the react-ance of each adjustable coaxial section vs. frequency;

FIG. 5 is a plot of the change of length of each coaxial section between the minimum and maximum operating frequency for various values of the characteristic impedance of each section; and

FIG. 6 is a cross-sectional view of the instant resonator.

Now referring to FIG. 1, the simplified output circuit of the instant resonator shown comprises two adjustable coaxial sections, A and A connected in series with each other and the plate 11 and ground contacts 12 of tube 10. Any conventional type of negative grid electron tube may be used for unit 10. The load resistance, R is shunted across the A coaxial section at points a and a. The general theory of operation as an amplifier is well known in the prior art and will be assumed without explanation except in so far as the effect of the tuning and loading is concerned.

Now referring to FIGS. 1 and 6, adjustable means, 21 and 22, are provided for changing the effective length of each coaxial section A and A i.e. these adjustable means achieve the desired resonant frequency. As shown, a pair of shorting bars, 23 and 24, slideable along the conductor walls, form end walls in coaxial sections A and A respectively. Axial adjustment of shorting bars, 23 and 24, is achieved by means of plunger rods, 25 and 26, of insulating material projecting out through supports 41 and 42. Short circuiting plungers, 25 and 26, are mechanically linked to common shaft 33. Tuning is accomplished by axial movement of the shaft; the loading adjustment is accomplished by rotation of the shaft.

It is to be noted in FIGURE 6 that use of suitable bypass condensers, 18 and 19, and insulator 17 isolates the DC. anode voltage from the wall conductors.

The instant invention provides a resonator that is continuously tunable over a prescribed band of frequencies by maintaining the following derived theoretical relationship between the reactances of each coaxial section over the frequency range.

For resonance:

Where:

X is the reactance of section A X is the reactance of section A X is the plate-to-ground reactance of the vacuum tube Since l+ 2= pg Therefore any finite value of Z and Z can be used except Z =Z =0, where Z is the characteristic impedance in ohms of coaxial section A and Z is the characteristic impedance of coaxial section A It is to be noted that the plate-to-ground reactance, X of vacuum tube 10 is a function of frequency. I, is a function of frequency and plate voltage swing. The plate voltage swing will normally remain constant for a given class of tube operation for different frequencies. A typical plate-to-ground reactance vs. frequency curve is shown in FIG. 2.

As the resonator is tuned over the prescribed band of frequencies, the degree of coupling (loading) is made couj l t y s lecting values of Z and Z such that AL =AL in accordance with the following theoretical relationship.

For proper loading:

Where P is the required power output E is the voltage drop across section X 1,, is the resonator current in the an plane.

Therefore, to achieve constant loading, it is necessary to determine values of Z and Z (characteristic impedance) so that: short circuiting plungers 25 and 26 of coaxial sections A and A can be mechanically linked together; the circuit can be tunable from f to fm and simultaneously, without changing the mechanical link, the voltage drop E remain constant.

The following procedure is used:

(1) The values of X vs. frequency are poltted as shown in FIG. 4. The values are obtained in accordance with Equation 4, and from a plot of resonator current, 1 vs. frequency shown in FIG. 3.

(2) From Equation 5, a curve of X vs. frequency is plotted as shown in FIG. 4.

(3) From an actual measurement of the amount of movement of plunger 25, or change of length of L between v and f for various values of Z a plot of AL vs. Z is made as shown in FIG. 5.

(4) Using FIG. 4 for values of X a plot is made of the change of length of L between f and f for various values of Z as shown in FIG. 5.

By selecting values of Z and Z from FIG. 5 such that AL =AL essentially constant loading over the prescribed tuning range from f to f can be obtained. For example, in FIG. 5 it is seen that for Z =4 ohms and Z =28 ohms, AL =AL =7.4 cm. These values are practical. However, it is to be noted that in selecting Z and Z other factors such as voltage gradient and stored energy must be considered.

Means of varying the degree of coupling without an appreciable detuning of the resonant circuit is accomplished in the following manner:

It is necessary to change the reactance of section A X for a given frequency; thus, an increase in X will result in an increased voltage across the load R But when reactance X is increased, reactance X must bedecreased by the same magnitude to maintain resonance; that is, to avoid detuning, AX =-AX (frequency constant). This relationship between the reactances of the two sections is accomplished by maintaining the following relationship between L and L FET- "22 sec? 5L2 s) Thus, Equation 6 is the relationship between L and L the length in meters of sections Z and Z respectively, required in order to maintain resonance while changing loading. Since the relationship in Equation 6 cannot be maintained exactly over a band of frequencies, a practical solution is to solve Equation 6 for the center frequency, F

It should be noted that plungers 25 and 26 can be operated independently to obtain proper loading when used as an output circuit, or to obtain proper matching when used as an input circuit. In such a case, there would be no specific relationship between the impedances of the 2 1 M Z sections, and Equation 6 would not necessarily ho While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as set forth in the appended claims.

What I claim is:

1. A coaxial resonator circuit comprising an electron tube having an anode, a ground contact and an anodeto-ground reactance, a load, a first and second coaxial section each having a reactance, said coaxial sections serially connected to each other and to said anode and to said'ground contact and to said load, adjustable means for each of said coaxial sections to cause the sum of the reactances of said first and second sections to equal said tube anode-to-ground reactance.

2. A coaxial resonator circuit for varying the degree of coupling to a load without appreciably detuning said circuit comprising: a vacuum tube of coaxial construction, a load, a first and second coaxial section connected in series with each other, short circuiting plunger means insertable in each of said coaxial sections, common means for driving said plungers, said first coaxial section connected to the anode of said tube and to said load, said second coaxial section connected to a ground contact point of said tube and to said load, said first and second coaxial sections coacting to provide essentially constant loading over the operating frequency tuning range by causing the change in length of said first section to be equal to the change in length of said second coaxial section.

References Cited UNITED STATES PATENTS 2,786,135 3/1957 Garrigus et al. 330154 X 2,917,712 12/1959 Smith et al. 330-56 3,124,764 3/ 1964 Stearns 33056 X ARTHUR GAUSS, Primary Examiner.

I. ZAZWORSKY, Assistant Examiner. 

1. A COAXIAL RESONATOR CIRCUIT COMPRISING AN ELECTRON TUBE HAVING AN ANODE, A GROUND CONTACT AND AN ANODETO-GROUND REACTANCE, A LOAD, A FIRST AND SECOND COAXIAL SECTION EACH HAVING A REACTANCE, SAID COAXIAL SECTIONS SERIALLY CONNECTED TO EACH OTHER AND TO SAID ANODE AND TO SAID GROUND CONTACT AND TO SAID LOAD, ADJUSTABLE MEANS 